JPH0525387B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a plasma processing apparatus, and in particular, the present invention relates to a plasma processing apparatus that uses plasma generated by microwave discharge,
High-efficiency plasma processing such as thin film formation, etching, sputtering, plasma oxidation, etc. on the sample surface,
The present invention also relates to a plasma processing apparatus suitable for large area processing.

[Conventional technology]

In conventional plasma processing equipment that uses plasma generated by microwave discharge in a magnetic field, the axial length of the discharge tube, which is a part of the discharge space, is larger than its inner diameter, and the maximum position of the axial magnetic field distribution is The microwave incidence end is shifted, and the plasma is divided on both sides of the maximum magnetic flux density position in the discharge tube, making it difficult for the plasma on the microwave incidence side to be pushed out toward the sample chamber. This results in a decrease in the efficiency of plasma generation on the side opposite to the microwave incidence side, which is effective for sample processing, and the position of maximum magnetic flux density. Furthermore, in order to improve this, if the maximum magnetic flux density position is generated near the microwave incident end of the discharge tube, it is necessary to maintain the magnetic flux density distribution shape of the discharge space on the sample chamber side before the improvement. Both the weight of the coil and its power supply capacity were required to be more than twice as large.

In addition, discharge tubes with a hemispherical shape and a flat plate window perpendicular to the direction of microwave incidence (traveling direction) are known, but these are difficult to prevent from traveling waves with respect to the electric field vibration plane of microwaves. There is a dielectric that forms a discharge tube (or discharge chamber) vertically when viewed, and the change in impedance seen from the microwave becomes quite large. For this reason, the reflectance of microwaves increases at the microwave incident end face of the discharge tube, making it difficult to improve plasma generation efficiency.

The detailed structure of the conventional example is shown in FIGS. 3 and 4. In FIG. 3, the axial length (height) h' of the discharge tube is compared with its inner diameter (diameter) φd. In case d, the maximum magnetic flux density position (approximately the center of the coil) and the tip of the discharge tube are clearly misaligned, and there is a problem that the plasma is split on both sides at the maximum magnetic field position, and the magnetic field is located at the position indicated by the broken line in the figure. The magnetic flux density distribution when the coil 1' is added is as shown by the broken line in FIG.

Figure 4 shows a hemispherical discharge tube whose tube length h'' is shorter than the discharge tube diameter φd, but at the microwave incidence end face, the flat plate insulator φd' faces almost perpendicular to the direction of microwave propagation. As a result, the impedance seen from the waveguide changes rapidly, which tends to increase reflected waves.

Regarding plasma processing equipment, please refer to JP-A-61-
It is disclosed in JP-A No. 256725, JP-A-61-256726, JP-A-59-3018, and the like.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not take into consideration the discharge tube dimensions, magnetic flux density distribution shape, and plasma generation area associated therewith, and has a problem in that the plasma generation efficiency is low, resulting in a large device and large power consumption.

An object of the present invention is to provide a plasma processing apparatus that can reduce power consumption by minimizing the plasma generation area necessary for processing and performing plasma processing without reducing the efficiency of microwave incidence into a discharge tube. There is a particular thing.

[Means for solving problems]

The above purpose includes an electron cycletron resonance magnetic field that is effective for plasma generation, has a magnetic flux density distribution that monotonically decreases from the microwave incidence end of the discharge tube toward the sample chamber, and has the axial length of the discharge tube equal to the inner diameter of the discharge tube. This can be achieved by making the discharge tube a convex conical shape, and by locating the microwave incident end of the discharge tube near the axial center of the magnetic field generating means.

[Effect]

Generally, in an air-core solenoid magnetic field coil, when the axial dimension (length) is longer than the average radius of the coil, the magnetic flux density distribution becomes horizontal instead of mountain-shaped. On the other hand, in magnetic field microwave discharge, effective microwave resonance absorption occurs near the electron cyclotron resonance magnetic field determined by the microwave frequency, generating plasma, and pushing the plasma toward the sample chamber side by the one-sided magnetic mirror effect. ing.

Therefore, the effective and minimum required magnetic field distribution shape includes the electron cyclotron resonance magnetic field,
It has a magnetic field gradient that monotonically decreases from the microwave incidence side to the sample chamber.

Therefore, in the present invention, as a structure that satisfies the above conditions and can be minimized in size, the length of the discharge tube provided inside the magnetic field coil is equal to or less than the inner diameter of the discharge tube, and the axial center of the magnetic field coil is In order to locate the microwave incident end of the discharge tube nearby and at the same time improve the efficiency of microwave incidence into the discharge tube, the discharge tube has a conical shape convex toward the microwave introduction side.

As a result, the microwave incidence end of the discharge tube is located near the maximum value of the magnetic flux density distribution shape having no horizontal magnetic field distribution, and the microwave reflectance is reduced because the discharge tube is of a convex shape. This makes it possible to minimize the magnetic field coil and to efficiently inject the coil power source and the microwave oscillator power source power into the plasma.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows an example in which the present invention is applied to a plasma processing apparatus that performs sample surface treatment (film formation) using magnetic field microwave discharge. Microwaves 4 are introduced through a waveguide 3 into a discharge tube 2 prepared for this purpose. The magnetic field coil 1 is connected to the discharge tube 2 and extends in the direction of the sample chamber 9, which generates plasma by excitation or ionization by electron cyclotron resonance using the microwave 4 and is equipped with a sample stage 8 that holds a sample 7 to be processed. The plasma is pushed out by the gradient of the magnetic field generated in the sample chamber 9, and the material gas 10 newly introduced in front of the sample 7 is excited or ionized by the plasma flow and transported to the surface of the sample 7. , is a plasma processing apparatus that generates a thin film having a composition of the plasma gas 6 and the material gas 10 on the surface of a sample.

FIG. 2 shows the magnetic flux density distribution in the axial direction from the discharge tube 2 to the sample stage 8 direction of this example.
The horizontal axis shows the axial distance, and the vertical axis shows the magnetic flux density. In the present invention, the magnetic flux density distribution shape is shown by the solid line in FIG. 2, and the position of the discharge tube is h (first
The broken line in FIG. 2 and the discharge tube position h' (FIG. 2) indicate the conventional magnetic flux density distribution and the conventional discharge tube position.

In FIG. 1, the inner diameter of the discharge tube 2 is φd,
If the length (height) is h, then it is a conical discharge tube that satisfies hd and has a convex shape on the microwave 4 incident side, and its tip is placed approximately at the center of the magnetic field coil 1. ing. The magnetic flux density distribution of the magnetic field coil 1 has a shape shown by the solid line in FIG. 2, and the microwave incident side end of the discharge tube 2 is approximately at the maximum magnetic flux density position. Therefore, if there is at least one electron cyclotron resonance magnetic flux density determined by the microwave frequency in the magnetic flux density that decreases almost monotonically in the direction of the sample chamber 9 from the maximum magnetic flux density position in FIG. The generated plasma is pushed toward the sample chamber 9 side by the magnetic field gradient and is effectively used.

However, as shown in the conventional example, when the axial length h' of the discharge tube is h'>d (inner diameter of the discharge tube) (Fig. 3).
h'> φd), the plasma generated or diffused closer to the microwave incidence end than the maximum magnetic flux density position is pushed toward the tip of the discharge tube, damaging the discharge tube and attenuating microwave propagation. , microwave power cannot be input to the plasma to be processed. In addition, in order to improve this magnetic flux density distribution shape, a magnetic field is monotonically decreased from the microwave incidence end of the discharge tube to the sample chamber 9 direction without changing the magnetic flux density distribution in the sample chamber 9 direction from the maximum magnetic flux density position before improvement. Then, the weight of the coil and the power capacity of the coil are approximately 2
More than twice as much is required. Furthermore, there are examples where the axial length of the discharge tube is less than the tube diameter, but since the discharge tube has a hemispherical shape or a flat insulator window, the axial cross section at the microwave incident end of the discharge tube is taken. Even in the case of a hemispherical discharge tube, the space factor of the dielectric on the microwave incidence surface is more than half (Fig. 4,
φd' dimension), the impedance seen from the microwave transmission system is such that the main electric field vibration surface of the microwave is in the direction along the axial cross section, so the surface with a large space factor suddenly changes in the direction of microwave propagation. It changes rapidly due to the appearance of This allows the microwave to reach the surface of the discharge tube before entering the plasma.
Or the amount reflected by the incident flat window increases,
There is a tendency that microwave power cannot be efficiently injected into the plasma.

This embodiment solves both of these problems at the same time, efficiently uses microwave power and magnetic field coil power, reduces the weight of the magnetic field coil, and changes the shape of the solenoid magnetic field coil to a one-turn magnetic field coil. By bringing them close together, the divergence rate of the magnetic flux density distribution can be increased, which has the effect that even samples having an outer diameter larger than the diameter of the discharge tube can be processed uniformly.

5 and 6 show other embodiments and application examples of the present invention. In FIG. 5, the waveguide 3 is connected to the discharge tube 2.
This is a plasma processing apparatus in which the magnetic field coil 1 is made as small as possible so as to comply with the following.

FIG. 6 shows an apparatus having an auxiliary magnetic field coil 12 for adjusting the divergent magnetic flux density distribution by the magnetic field coil 1. FIG.

〔Effect of the invention〕

According to the plasma processing apparatus of the present invention described above, the discharge tube into which the discharge gas is introduced and which forms part of the discharge space has a longitudinal dimension that is equal to or smaller than the inner diameter (diameter) of the discharge tube. , and the microwave incidence end of the discharge tube is located near the axial center of a magnetic field generating means that has a convex conical shape on the microwave introduction side and generates a magnetic field within the discharge space of the discharge tube. This makes it possible to minimize the plasma generation area required for processing and perform plasma processing without reducing the efficiency of microwave injection into the discharge tube, reducing power consumption. effective.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a plasma processing apparatus showing an embodiment of the present invention, FIG. 2 is a diagram showing the axial magnetic flux density distribution of the plasma processing apparatus, and FIGS. 3 and 4 are each a diagram showing conventional plasma processing. A cross-sectional view showing the device;
5 and 6 are sectional views of plasma processing apparatuses showing other embodiments of the present invention, respectively. 1... Magnetic field coil, 2... Discharge tube, 3... Waveguide, 4... Microwave, 6... Plasma generation gas, 7... Sample, 8... Sample stage, 9... Sample chamber,
10...Material gas, 11...Vacuum exhaust, 12...
Auxiliary magnetic field coil.

Claims (1)

[Scope of Claims] 1. A discharge tube into which a discharge gas is introduced and which forms a part of a discharge space, a magnetic field generating means for generating a magnetic field within the discharge space of the discharge tube, and a microwave source that generates microwaves within the discharge space. a means for introducing the discharge tube;
and a sample chamber having a sample stage for holding a sample to be processed, wherein the longitudinal dimension of the discharge tube is approximately equal to or smaller than the inner diameter (diameter) of the discharge tube; Moreover, it has a convex conical shape on the microwave introduction side, and
A plasma processing apparatus characterized in that a microwave incident end of the discharge tube is located near the axial center of the magnetic field generating means. 2. The plasma processing apparatus according to claim 1, wherein the outer diameter of the sample held on the sample stage in the sample chamber is larger than the inner diameter of the discharge tube.